Remove unfetch

[talentlessguy]

Pre-flight checklist

• I have read the Contributing Guidelines on pull requests.
• Commit messages follow the conventional commits spec
• If this is a code change: I have written unit tests.
• If this changes code in a published package: I have run pnpm changeset to create a changeset JSON document appropriate for this change.
• If this is a new API or substantial change: the PR has an accompanying issue (closes #0000) and the maintainers have approved on my working plan.

Motivation

since near-js least supported node version is v20, the polyfill could be safely dropped. React Native, and all edge runtimes all support fetch. There is no need to keep the polyfill anymore.

Test Plan

unit tests

Related issues/PRs

none

[changeset-bot]

🦋 Changeset detected

Latest commit: 6fc2893

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 5 packages

Name	Type
@near-js/accounts	Patch
@near-js/client	Patch
@near-js/providers	Patch
near-api-js	Patch
@near-js/wallet-account	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[talentlessguy]

for whatever reason typescript says that fetchMock once is not defined, even though it is. I suspsect this is something to do with Jest or incorrectly configured typescript compiler (probably the first)

 FAIL  test/fetch_json_error.test.ts
  ● Test suite failed to run

    test/fetch_json_error.test.ts:16:19 - error TS2339: Property 'once' does not exist on type 'FetchMockJest'.

    16         fetchMock.once(RPC_URL, 500, '');
                         ~~~~
    test/fetch_json_error.test.ts:24:19 - error TS2339: Property 'once' does not exist on type 'FetchMockJest'.

    24         fetchMock.once(RPC_URL, 408, '');
                         ~~~~
    test/fetch_json_error.test.ts:33:19 - error TS2339: Property 'once' does not exist on type 'FetchMockJest'.

    33         fetchMock.once(RPC_URL, 400, '');
                         ~~~~
    test/fetch_json_error.test.ts:41:19 - error TS2339: Property 'once' does not exist on type 'FetchMockJest'.

    41         fetchMock.once(RPC_URL, 503, '');
                         ~~~~